Marker for optical tracking, optical tracking system, and optical tracking method

ABSTRACT

The present disclosure provides a marker with a pattern formed thereon, which includes an optical system. At least a part of the pattern that uniquely appears depending on a direction in which the pattern is viewed from an outside of the marker through the optical system, is visually identified from the outside of the marker. The pattern includes a plurality of rows of binary-coded sequences. The binary-coded sequence of each of the plurality of rows includes aperiodic sequences that are repeatedly arranged. The aperiodic sequences included in the binary-coded sequence of one row of the plurality of rows are different from the aperiodic sequences included in the binary-coded sequence of another row of the plurality of rows, and each of the aperiodic sequences includes a plurality of sub-sequences that are arranged in a predetermined order.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Korean Patent ApplicationNo. 10-2016-0101377 filed on Aug. 9, 2016, the entire subject matter ofwhich is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a marker for measuring a location anda posture of a target, and further relates to an optical tracking systemand a tracking method using the same.

The present disclosure is derived from research conducted as a part ofthe Robot Industry Fusion Core Technology Development Project of theMinistry of Trade, Industry and Energy. [Project No. 10062800, ProjectTitle: Development of Practical Technology of Medical Imaging basedBrain Surgery Robot System through Clinical Trial]

BACKGROUND ART

An optical tracking system may be used for tracking a target. Recently,in order to process precise surgery while minimizing a risk of theoccurrence of surgical errors, a method has been used that tracks thelocation (or coordinates) and the posture (or orientation) of a surgicalrobot or a surgical instrument and utilizes the tracking result forsurgery. The location of a target, for example, may be defined asspatial coordinates, such as coordinates on the X, Y, and Z axes of anorthogonal coordinate system. The posture of a target may be defined asa roll, pitch, or yaw. In order to accurately track a target, it isimportant to accurately recognize the location and the posture of thetarget, which correspond to six degrees of freedom as described above.

In the optical tracking system, for example, after attaching a referencebody, such as a marker, to the target, the marker is tracked in order todetermine the location and the posture of the target. For example, thelocation and the posture of a target may be measured by attaching to thetarget a structure, to which three or more markers are attached. Themethod of using three or more markers may cause a problem in which it isdifficult to reduce the size of the tracking reference body. Inparticular, when a plurality of markers is attached to a tool, such as asurgical instrument, which is directly navigated by a user, the user maybe interrupted or inconvenienced due to its size and weight while usingthe instrument.

SUMMARY

An aspect of the present disclosure is to provide a marker for opticaltracking, which can be lightened and miniaturized.

Another aspect of the present disclosure is to provide an opticaltracking system and a method for measuring both the location and theposture of a target by using a light or small marker. For example, thepresent disclosure provides an optical tracking system and a trackingmethod for tracking the location and the posture of a target to whichone or more markers are attached.

According to one aspect of the present disclosure, a marker with apattern formed thereon may include an optical system, wherein: at leasta part of the pattern that uniquely appears depending on a direction inwhich the pattern is viewed from an outside of the marker through theoptical system, is visually identified from the outside of the marker;the pattern includes a plurality of rows of binary-coded sequences; thebinary-coded sequence of each of the plurality of rows includesaperiodic sequences that are repeatedly arranged; the aperiodicsequences included in the binary-coded sequence of one row of theplurality of rows are different from the aperiodic sequences included inthe binary-coded sequence of another row of the plurality of rows; andeach of the aperiodic sequences includes a plurality of sub-sequencesthat are arranged in a predetermined order.

According to one embodiment, the plurality of rows of binary-codedsequences may include a first binary-coded sequence and a secondbinary-coded sequence that are adjacent in a column direction, and anumber of bits of each of the sub-sequences included in the firstbinary-coded sequence is different from a number of bits of each of thesub-sequences included in the second binary-coded sequence.

According to one embodiment, the pattern further include a thirdbinary-coded sequence positioned in a m-th row from the firstbinary-coded sequence in the column direction and a fourth binary-codedsequence positioned in the m-th row from the second binary-codedsequence in the column direction, wherein the aperiodic sequenceincluded in the third binary-coded sequence may be equal to theaperiodic sequence included in the first binary-coded sequence, and theaperiodic sequence included in the fourth binary-coded sequence may beequal to the aperiodic sequence included in the second binary-codedsequence, and wherein m may be a natural number of 2 or more.

According to one embodiment, the pattern may include: a first sequencegroup including the first and second binary-coded sequences; a secondsequence group including the third and fourth binary-coded sequences;and a meta-sequence configured to separate the first and second sequencegroups from each other.

According to one embodiment, the meta-sequence may be different from thebinary-coded sequences that are included in the first and secondsequence groups.

According to one embodiment, the meta-sequence may be a sequence inwhich different binary codes are alternately repeated, or may becomprised of only the same binary code.

According to one embodiment, the marker may further include a patternplane on which the pattern is formed, and different binary codes thatare included in the binary-coded sequences of the pattern formed on thepattern plane are made of materials that have different reflectivitiesfrom each other.

According to one embodiment, the marker may further include a patternplane on which the pattern is formed, and the optical system may includea lens, wherein the pattern is formed in a portion where a focal pointof the lens is formed on the pattern plane.

According to one embodiment, the pattern plane may have a flat or curvedsurface, and the lens may allow the focal point to be formed on the flator curved surface.

According to one embodiment, the aperiodic sequence may be a PRBS(Pseudo-Random Binary Sequence) or De Bruijn Sequence.

According to one embodiment, if at least a part of the pattern iscaptured as a pattern image in the outside of the marker, a size of aregion where at least a part of the pattern is captured on the patternimage varies with at least one of a distance from a location in whichthe pattern image is captured to the marker or a location of the marker.

According to another aspect of the present disclosure, an opticaltracking system may include: one or more markers on which a pattern isformed; one or more capturing units that is configured to include one ormore capturing elements that obtains a pattern image of the pattern; anda processor configured to track locations and postures of the one ormore markers based on information that is extracted from at least a partof the pattern included in the pattern image, wherein: the patternincludes a plurality of rows of binary-coded sequences; the binary-codedsequence of each of the plurality of rows includes aperiodic sequencesthat are repeatedly arranged; the aperiodic sequences included in thebinary-coded sequence of one row of the plurality of rows are differentfrom the aperiodic sequences included in the binary-coded sequence ofanother row of the plurality of rows; and each of the aperiodicsequences includes a plurality of sub-sequences that are arranged in apredetermined order.

According to one embodiment, the optical tracking system extracts one ormore sequence blocks from the pattern image and then tracks the one ormore markers, and wherein the one or more sequence blocks include a partof the plurality of rows of binary-coded sequences.

According to one embodiment, the one or more sequence blocks have a sizeof j×1 in which j denotes a number of binary-coded sequences that areincluded in the one or more sequence blocks and 1 denotes a number ofbits of a longest sub-sequence among the plurality of sub-sequencesincluded in the one or more sequence blocks.

According to one embodiment, the processor determines postures or IDs ofthe one or more markers based on the one or more sequence blocks.

According to one embodiment, the part of the plurality of rows ofbinary-coded sequences are sub-sequences that are included in each ofthe plurality of rows of binary-coded sequences, and the processordetermines a location of a sub-pattern represented by the one or moresequence blocks in the pattern based on the sub-sequences, anddetermines the postures of the one or more markers based on the locationof the sub-pattern.

According to one embodiment, the part of the plurality of rows ofbinary-coded sequences are sub-sequences that are included in each ofthe plurality of rows of binary-coded sequences, and the processordetermines location information on the one or more sequence blocks inthe plurality of binary-coded sequences based on the sub-sequences, anddetermines the IDs of the one or more markers based on the locationinformation.

According to one embodiment, the one or more capturing units may includetwo or more capturing units, or the one or more capturing elements mayinclude two or more capturing elements. In addition, the processordetermines the locations of the one or more markers based ontriangulation by using pattern images that are obtained by the two ormore capturing units or by the two or more capturing elements.

According to one embodiment, the processor determines the locations ofthe one or more markers based on central coordinates of a region of thepattern on each of the pattern images and triangulation by using ageometric relationship between directions in which the two or morecapturing units or the two or more capturing elements view the one ormore markers.

According to one embodiment, the processor determines the locations ofthe one or more markers based on a size of a region of the pattern andcentral coordinates of the pattern region, on the pattern image obtainedby the capturing units.

According to one embodiment, the one or more markers may include twomarkers that have a predetermined geometric relationship, and thecapturing units capture pattern images of patterns that are formed onthe two markers, respectively. In addition, the processor determines thelocations of the two markers based on the predetermined geometricrelationship and a relationship between a location of at least a part ofthe patterns on the pattern images and a location of at least a part ofthe pattern on each of the markers.

According to one embodiment, the plurality of rows of binary-codedsequences include a first binary-coded sequence and a secondbinary-coded sequence that are adjacent in a column direction, and anumber of bits of each sub-sequence included in the first binary-codedsequence is different from a number of bits of each sub-sequenceincluded in the second binary-coded sequence.

According to one embodiment, the pattern further includes a thirdbinary-coded sequence positioned in a m-th row from the firstbinary-coded sequence in the column direction and a fourth binary-codedsequence positioned in the m-th row from the second binary-codedsequence in the column direction, wherein the aperiodic sequenceincluded in the third binary-coded sequence may be equal to theaperiodic sequence included in the first binary-coded sequence and theaperiodic sequence included in the fourth binary-coded sequence may beequal to the aperiodic sequence included in the second binary-codedsequence, and wherein m is a natural number of 2 or more.

According to one embodiment, the one or more markers include a firstlens, and the pattern is implemented on a pattern plane on which a focalpoint of the first lens is formed. In addition, the one or morecapturing units include a second lens that is configured such that atleast a part of the pattern, which is visually identified from the oneor more markers in a direction in which the capturing units view the oneor more markers through the first lens, is captured on the one or morecapturing elements, and obtains a pattern image of at least a part ofthe pattern in a focal length of the second lens.

According to one embodiment, the optical tracking system may furtherinclude a light source configured to emit light onto the one or moremarkers in order to enhance the light incident on the second lensthrough the first lens with respect to at least a part of the pattern.

According to still another aspect embodiment of the present disclosure,an optical tracking method for tracking a marker on which a pattern isformed is disclosed. The method may include: obtaining, by one or morecapturing elements included in one or more capturing units, a patternimage of at least a part of the pattern; and proceeding, by a processor,information extracted from at least a part of the pattern included inthe pattern image and tracking a location and a posture of the marker,wherein: the pattern includes a plurality of rows of binary-codedsequences; the binary-coded sequence of each of the plurality of rowsincludes aperiodic sequences that are repeatedly arranged; the aperiodicsequences included in the binary-coded sequence of one row of theplurality of rows are different from the aperiodic sequences included inthe binary-coded sequence of another row of the plurality of rows; andeach of the aperiodic sequences includes a plurality of sub-sequencesthat are arranged in a predetermined order.

According to one embodiment, the tracking the location and the postureof the marker includes extracting one or more sequence blocks from thepattern image, and the one or more sequence blocks have a size of j×1 inwhich j denotes a number of binary-coded sequences that are included inthe one or more sequence blocks and 1 denotes a number of bits of alongest sub-sequence among the sub-sequences included in the one or moresequence blocks.

According to one embodiment, the tracking the location and the postureof the marker includes determining the posture of the marker based onthe one or more extracted sequence blocks.

According to one embodiment, the determining the posture of the markerincludes: determining a location of a sub-pattern represented by the oneor more sequence blocks in the pattern based on the sub-sequences thatare included in each of the plurality of rows of binary-coded sequencesthat are included in the one or more sequence blocks; and determiningthe posture of the marker based on the determined location of thesub-pattern.

According to one embodiment, the one or more capturing units may includetwo or more capturing units, or the one or more capturing elements mayinclude two or more capturing elements. In addition, the tracking thelocation and the posture of the marker comprises determining thelocation of the marker based on triangulation by using pattern imagesthat are obtained by the two or more capturing units or by the two ormore capturing elements.

According to one embodiment, the determining the location of the markerbased on the triangulation includes determining the location of themarker based on central coordinates of the pattern region on each of thepattern images and triangulation by using a geometric relationshipbetween directions in which the two or more capturing units or the twoor more capturing elements view the marker.

A computer-readable recording medium according to an exemplaryembodiment of the present disclosure may store a program that mayexecute operations of the optical tracking method according to anexemplary embodiment of the present disclosure.

The marker, according to one embodiment of the present disclosure, maybe implemented to be small.

In addition, according to the optical tracking system by using a markerin accordance with one embodiment of the present disclosure, it ispossible to measure, by using one or more markers, the location and theposture of a target having the attached markers, which correspond to sixdegrees of freedom.

Furthermore, according to the optical tracking system by using a markerin accordance with one embodiment of the present disclosure, thedistance in which the tracking can be made may increase, and it ispossible to reduce a tracking error that occurs because a part of thepattern included in the marker is obscured.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the inventive aspects of this disclosure will beunderstood with reference to the following detailed description, whenread in conjunction with the accompanying drawings.

FIG. 1 describes an optical tracking system used for surgery, accordingto one embodiment of the present disclosure.

FIG. 2 is a surgical instrument where a marker is attached and used,according to one embodiment of the present disclosure.

FIG. 3 depicts a block diagram of an optical tracking system including amarker, according to one embodiment of the present disclosure.

FIG. 4 illustrates a block diagram of an optical tracking systemincluding a marker, according to another embodiment of the presentdisclosure.

FIG. 5 is a diagram of a pattern, according to one embodiment of thepresent disclosure, according to one embodiment of the present.

FIG. 6 depicts a diagram that explains a pattern, according to oneembodiment of the present disclosure.

FIG. 7 illustrates a diagram of a configuration of a De Bruijn Sequence.

FIG. 8 is a diagram that shows a binary-coded sequence in which a DeBruijn Sequence is repeated.

FIG. 9 describes a diagram that explains a method of implementing apattern that is formed on the marker by using a De Bruijn Sequence ofB(2,3)-1 and a De Bruijn Sequence of (2,2), according to one embodimentof the present disclosure.

FIG. 10 depicts a diagram showing a method for implementing atwo-dimensional pattern by using a single long horizontal pattern thatis formed according to one embodiment of the present disclosure.

FIG. 11 illustrates a diagram that explains a method for determining theposture and ID of a marker based on a pattern image of the marker, whichis captured in a capturing unit of the optical tracking system,according to one embodiment of the invention.

FIG. 12 is a flowchart of a method for tracking a marker in an opticaltracking system, according to one embodiment of the present disclosure.

FIG. 13 is a flowchart of a method for tracking the location and theposturea location and a posture of a marker in an optical trackingsystem, according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are only examples that areillustrated for the purpose of explaining the present disclosure. Theembodiments of the present disclosure may be conducted in variousmanners, and the present disclosure shall not be construed to be limitedto the embodiments described below or to the detailed description of theembodiments.

The term “unit” used in the present embodiments refers to a softwareelement or a hardware element, such as FPGA (field-programmable gatearray), ASIC (application specific integrated circuit), etc. However,the “unit” is not limited to hardware and software. The “unit” may beconfigured to be in a storage medium that can be addressed, and may beconfigured to reproduce one or more processors. Accordingly, as anexample, the “unit” includes elements, such as software elements,object-oriented software elements, class elements, task elements, etc.,processors, functions, attributes, procedures, subroutines, program codesegments, drivers, firmware, micro-codes, circuits, data, databases,data structures, tables, arrays, and variables. Functions that areprovided in the elements and “unit” may be combined into fewer elementsand “units,” or may be further divided into additional elements and“units.”

All the technical terms and scientific terms in the presentspecification include meanings or definitions that are commonlyunderstood by those of ordinary skill in the art unless otherwisedefined. All terms in the present specification are selected for thepurpose of describing the present disclosure more clearly, and are notselected to limit the scope of the present disclosure.

The singular expressions that are described in the present specificationmay encompass plural expressions unless otherwise stated, which will bealso applied to the singular expressions recited in the claims.

The expressions, such as “first,” “second,” etc., which are shown invarious embodiments of the present disclosure, are used to separate aplurality of elements from each other, and are not intended to limit anorder or importance of the corresponding elements.

The expressions, such as “include” or “have,” which are used in thepresent specification, should be appreciated as open-ended terms thatinclude a possibility of including other embodiments unless particularlyotherwise stated in the phrase or sentence that contains thecorresponding expressions.

In the present specification, the expression “based on” will be used todescribe one or more factors that affect an act or operation of adecision or determination that is described in the phrase that containsthe corresponding expression, and does not exclude additional factorsthat affect the act or operation of the decision or determination.

In the present specification, the description that one element is“connected,” or “coupled” to another element should be appreciated toindicate that one element may be directly connected, or coupled, toanother element, and should be further understood that a new element maybe interposed between one element and another element.

Hereinafter, the embodiments of the present disclosure will be describedin detail with reference to the accompanying drawings. The samereference numeral will be used for the same element throughout thedrawings, and a duplicate description of the same element will beomitted.

<Optical Tracking System>

FIG. 1 describes an optical tracking system used for surgery, accordingto one embodiment of the present disclosure. As shown, a surgeon 140 mayproceed with surgery for a patient 160 by using a surgical instrument150 and the optical tracking system, which includes a capturing unit130. A marker 110 may be attached to the surgical instrument 150 that isused by the surgeon 140, and another marker 120 may be attached to atarget, such as an affected portion of the patient 160. The capturingunit 130 of the optical tracking system may capture and obtain a patternimage for the whole pattern or a part of a pattern formed on the marker110 or 120. The pattern image may be captured in a partial region in aframe of a captured image that is output by an image sensor of thecapturing unit 130.

When the pattern image is obtained, one or more sub-patterns may beextracted from the pattern image as a basic unit constituting thepattern of the marker. According to some embodiments, locations of theone or more extracted sub-patterns in the entire pattern may bedetermined, and the posture of the marker 110 or 120 may be determinedbased on the determined the locations of the sub-patterns in the entirepattern. In this case, the posture of the marker 110 or 120 may bereferred to a relative three-dimensional direction or orientation of themarker 110 or 120 with respect to the capturing unit 130.

In addition, according to one embodiment, a location of one of themarkers 110 and 120 in a three-dimensional space may be determined basedon a size and coordinates of at least one pattern image in a capturedimage that is captured by one or more capturing units 130 that includeone or more capturing elements.

In some embodiments, the capturing unit 130 may include two or morecameras, and a location of one of the markers 110 and 120 may bedetermined by using triangulation based on the pattern images capturedby the cameras.

According to one embodiment, two markers 110 and 120 that have apredetermined geometric relationship may be attached to a single target.In this case, the locations of the markers 110 and 120 in thethree-dimensional space may be determined based on the predeterminedgeometric relationship of the markers 110 and 120 and a relationshipbetween a location of at least a part of the pattern on the patternimage and a location of at least a part of the pattern (e.g., acorresponding part) on each of the markers 110 an 120.

When the location and the posture of the marker 110 or 120 are obtainedas described above, the location and the posture of a target to whichthe marker 110 or 120 is attached may be determined based on a geometricrelationship between the marker 110 or 120 and the target to which themarker 110 or 120 is attached.

According to some embodiments, one embodiment the location and theposture of the target corresponding to six degrees of freedom may bedetermined by using one or more markers in the optical tracking system,which will be described in detail below.

FIG. 2 depicts a surgical instrument 230 to which a marker 210 isattached, according to one embodiment of the present disclosure. In oneembodiment of the optical tracking system of the present disclosure,even in the case where a single marker 210 is attached to the surgicalinstrument 230 as a target, the location and the posture of the targetmay be tracked based on a pattern formed on the marker 210. Therefore, alight or small marker may be attached to the surgical instrument 230,and a surgeon may proceed with surgery by using the surgical instrument230 with the marker attached without concerning about a size or weightof the marker.

In one embodiment, the marker may be attached to or detached from atarget to be tracked. As shown in FIG. 2, when preparing for a surgeryprocess, the marker 210 may be sterilized before it is attached to thesurgical instrument 230. In this case, since only a single marker 210needs to be attached to the surgical instrument 230, theattachment/detachment process may be simplified. In addition, since onlya single marker 210 needs to be sterilized, it is possible to reduce thetime and the effort required for the surgery preparation including adisinfection process. As the number of targets to which the marker isattached for surgery increases, the number of markers to be attached ordetached may increase. Thus, in the case of using a single marker, it ispossible to reduce time and cost for the surgery preparation.

Although the marker and the optical tracking system, according to thepresent disclosure, are used in a surgery of a patient by a surgeon inthe embodiments described above, they may also be used in various otherinstances for determining the location and the posture of a target byusing a marker. For example, the marker and the optical tracking system,according to the present disclosure, may be used for determining thelocation and the posture of a surgical instrument that is attached to asurgical robot when a patient undergoes surgery using the surgicalrobot. In another example, the marker and the optical tracking system,according to the present disclosure, may be used for determining thelocation and the posture of a specific instrument and/or target when aspecific operation is performed with respect to the target using theinstrument by an operator or surgical robot. The various embodiments ofthe marker and the optical tracking system of the present disclosure,which have been described through the examples of FIGS. 1 and 2, will bedescribed in more detail below.

FIG. 3 depicts a block diagram of an optical tracking system 300,according to one embodiment of the present disclosure. The opticaltracking system 300 may include a marker 310, a capturing unit 330, anda processor 350. The marker 310 may include a pattern plane 311 on whicha pattern is formed and an optical system 312, such as lenses, that isconfigured to allow at least a part of the pattern, which uniquelyappears according to a viewing direction from the outside of the marker,to be identified (or visually recognized) from the outside of the marker310. In one embodiment, when the marker 310 belongs to the field of view(FOV) of the capturing unit 330 and the optical system 312 is arrangedtoward the capturing unit 330, the capturing unit 330 may capture atleast a part of the pattern that is identified through the opticalsystem 312.

The capturing unit 330 may include lenses and capturing elements thatcan capture and obtain a pattern image including at least a part of thepattern. Any type of capturing element may be provided, which isconfigured to obtain a captured image for any object, and the capturingelement, for example, may include a CCD (charge-coupled device), CMOS(complementary metal-oxide semiconductor) image sensor, or the like.

According to one embodiment, the capturing unit 330 may include aplurality of capturing elements 332 and 334. The capturing elements 332and 334 may obtain pattern images of the marker 310 identified throughthe respective lenses 331 and 333. The capturing elements 332 and 334may be disposed at an angle to obtain a pattern image including at leasta part (or the same region) of the pattern that is formed on the marker310. Even though the number of the capturing elements is 2 (two) in FIG.3, the capturing unit 330 may include three or more of capturingelements.

According to some embodiments, the optical tracking system 300 mayfurther include one or more light sources for emitting the light ontothe marker 310 or the pattern in order to enhance the light incident onthe lenses 331 and 333 through the optical system 312 so that thepattern can be properly identified from the outside of the marker 310.

In one embodiment, the light source may be installed in the outside ofthe marker 310. In this case, the marker 310 may operate as a passivemarker. If the marker 310 operates as a passive marker, the capturingunit 330 may include one or more light sources 335 and 337 to emit thelight onto the marker 310. As shown in FIG. 3, the light from the lightsource 335 may be reflected by a beam splitter 338 and be then emittedonto the marker 310 through the lens 331. The light from the other lightsource 337 may be reflected by a beam splitter 339 and be then emittedonto the marker 310 through the lens 333. In this configuration, thelight that is reflected by the beam splitter 338 or 339 and is thenemitted onto the marker 310 through the lens 331 or 333 from thecapturing unit 330 and the light that is reflected by the pattern of themarker 310 and is then received through the lens 331 or 333 of thecapturing unit 330 may travel through the same path with respect to thelenses 331 and 333. In this case, since the amount of the light that isreflected by the marker 310 and is then received by the capturing unit330 may increase, the capturing elements 332 and 334 may capture evenclearer pattern images.

According to another embodiment, the light source may be installed toemit the light to the front or back surface of the pattern plane 311inside the marker 310. In this case, the marker 310 may operate as anactive marker. In addition, the light sources 335 and 337 and the beamsplitters 338 and 339, which are installed in the capturing unit 330 asshown in FIG. 3, may be omitted.

The processor 350 may be configured to receive the pattern imageobtained in the capturing unit 330, and may determine the location andthe posture of the marker 310 based on the received pattern image. Inone embodiment, the processor 350 may determine the location of themarker 310 based on the size of at least a part (or region) of thepattern contained in the pattern image and the central coordinates ofthe region, or may determine the location of the marker 310 by usingtriangulation. In addition, the processor 350 may determine a locationof each of the sub-patterns, which constitute the pattern, in the entirepattern based on the pattern image, and may determine the posture of themarker 310 based on the locations of the sub-patterns. The method fordetermining the location and the posture of the marker 310 will bedescribed in more detail below.

In one embodiment, if the optical tracking system 300 operates in asurgical system, such as a surgical navigation system, the marker 310may be attached to one or more targets that include a surgicalinstrument, a part of a surgical robot, or an affected portion of apatient. In addition, in the case of using a plurality of markers, thelocations and postures of the markers may be tracked at the same time orsequentially. In this case, the processor 350 may distinguish themarkers attached to the respective targets based on IDs of the markersin order to track the locations and postures of the markers. Accordingto one embodiment, the processor 350 may extract an ID of the marker 310from the pattern image. The method for extracting and obtaining an ID ofthe marker 310 will be described in more detail later.

According to another embodiment, as shown in FIG. 4, the opticaltracking system 400 may include a plurality of capturing units 430 and440. The directions or angles of the capturing units 430 and 440 towardthe marker may be configured such that the respective capturing units430 and 440 can obtain pattern images for the same region of the patternformed on the marker 310. Even though the number of the capturingelements is 2 (two) in FIG. 4, the capturing unit 330 may include threeor more of capturing elements.

According to one embodiment, when the marker 310 operates as a passivemarker, the capturing units 430 and 440 may include light sources 433and 443, respectively, which can emit the light onto the marker 310. Inthis case, the light emitted from the light source 433 may be reflectedby a beam splitter 434 and be then transferred to the marker 310 througha lens 431. In addition, the light emitted from another light source 443may be reflected by a beam splitter 444 and be then transferred to themarker 310 through a lens 441.

The processor 450 may determine the location and the posture of themarker 310 based on the information extracted from at least a part ofthe pattern, which is included in the pattern image obtained by thecapturing elements 432 and 442 in the respective capturing units 430 and440. A method for determining the location and the posture of the marker310 by using a pattern image is executed in the same manner as themethod described above, which will be also described in more detailbelow.

According to another embodiment, the optical tracking system may tracklocations and postures of two markers having a predetermined geometricrelationship between them. The optical tracking system may obtainpattern images of patterns formed on two markers, respectively, througha single capturing element. The locations of two markers may bedetermined based on the predetermined geometric relationship and arelationship between the location of at least a part of the pattern onthe pattern image and the location of at least the corresponding part ofthe pattern on each of markers. The posture of the marker may bedetermined in the same manner as that described above.

<Marker>

The marker 310 may be attached to a target of which the location and theposture are measured by the optical tracking system 300 or 400, or maybe implemented by the whole or a part of the target. The location andthe posture of the target to which the marker 310 is attached may bemeasured by measuring the location and the posture of the marker 310. Inone embodiment, the marker 310 may include the pattern plane 311 and theoptical system 312, such as lenses, as described with reference to FIGS.3 and 4 above.

According to some embodiments, the marker 310 may be implemented byusing a material, such as resin, aluminum, or the like, which is a lightmaterial and is not damaged by medical substances, such as adisinfectant. When the marker 310 is attached to an instrument or deviceused for surgery, the marker 310 may be sterilized before it is used inthe surgery. In this case, the marker 310 is required to be implementedby using a material that is not damaged by the disinfectant.

The marker 310 may have an outer shape to allow the pattern plane 311and the optical system 312, such as lenses, to be easily installed.According to one embodiment, the marker 310 may have a cylindricalshape. If the marker 310 has a cylindrical shape, the optical system 312may be installed on one side of the cylindrical shape, and the patternplane 311 may be installed on the other side that faces the one side onwhich the optical system 312 is installed. In this configuration, apattern formed on the pattern plane 311 may be visually identifiedthrough the body of the cylinder and then through the optical system 312from the outside. According to another embodiment, the marker 310 mayhave a spherical or cubic shape. If the marker 310 has a sphericalshape, the pattern plane 311 on which the pattern is formed may beimplemented in at least a portion of the inner surface or outer surfaceof the sphere, and the optical system 312 may be implemented in anotherportion that faces the pattern plane 311 on the inner surface of thesphere.

Since the pattern is formed such that the location of each of thesub-patterns is uniquely determined throughout the entire pattern, theinformation on the location of each sub-pattern in the entire patternmay be extracted from the pattern image of the pattern. In addition, thepattern may be formed so as to provide the ID of the marker 310.

FIG. 5 shows a pattern 500, according to one embodiment of the presentdisclosure. In one embodiment, the pattern 500 may be formed byarranging one or more horizontal patterns (e.g., horizontal patterns510, 520, and 530) in a column direction. In this embodiment, it isassumed that the pattern 500 is formed by arranging three horizontalpatterns 510, 520, and 530 in the column direction in the presentembodiment. As shown, the horizontal patterns 510, 520, and 530 mayinclude sequence groups 511, 521, and 531, respectively, which include aplurality of rows of binary-coded sequences, respectively. According toone embodiment, each of the binary-coded sequences included in thesequence groups 511, 521, and 531 may include aperiodic sequences thatare repeatedly arranged.

Here, the “aperiodic sequences that are repeatedly arranged” mayindicate that the respective aperiodic sequences internally have amaximized auto-correlativity (the same sub-sequence is not shown twotimes or more in a single aperiodic sequence) and a deterministicrandomness (the unique location of each sub-sequence is predetermined ina single aperiodic sequence), whereas there is a minimizedcross-correlativity (different aperiodic sequences can be surelydistinguished from each other) between the aperiodic sequences and suchaperiodic sequences may be repeated two times or more in a singlebinary-coded sequence.

According to one embodiment, each aperiodic sequence may include aplurality of sub-sequences arranged in a predetermined order. Forexample, each aperiodic sequence may be a Pseudo-Random Binary Sequence(PRBS), and more specifically, may be a De Bruijn Sequence. In thiscase, the “aperiodic sequence,” as described above, may mean that it hasa maximized auto-correlativity or a plurality of sub-sequences includedin the corresponding sequence is not arranged in a periodic manner. Theconfiguration of such an aperiodic sequence will be described in moredetail below.

According to one embodiment, the horizontal patterns 510, 520, and 530may include meta-sequence groups 512, 522, and 532 that can separateadjacent sequence groups from each other among the sequence groups 511,521, and 531. Each of the meta-sequence groups 512, 522, and 532 mayinclude one or more meta-sequences.

The meta-sequence may be distinguished from the binary-coded sequenceincluded in the sequence groups. If the sequence groups 511, 521, and531 are formed such that adjacent sequence groups are separated fromeach other in the pattern 500, the meta-sequence groups 512, 522, and532 may be omitted in the pattern 500.

According to one embodiment, the meta-sequence may be a periodicsequence that has a minimized auto-correlativity (one sub-sequence isrepeated in the meta-sequence) and a maximized cross-correlativity.

According to another embodiment, the meta-sequence may be an aperiodicsequence that is not used in the sequence groups.

Although FIG. 5 illustrates that the meta-sequence is disposed toseparate the sequence groups from each other in the horizontaldirection, the meta-sequence may be disposed to separate the sequencegroups from each other in a vertical direction, according to oneembodiment. In another embodiment, the meta-sequence may be disposed toseparate the sequence groups from each other in horizontal and verticaldirections.

FIG. 6 is a diagram that shows a detailed configuration of two adjacenthorizontal patterns 510 and 520 in the pattern 500. According to oneembodiment, each of the horizontal patterns 510 and 520 may includesequence groups 511 and 521, respectively, and each of the sequencegroups 511 and 521 includes a plurality of rows of binary-codedsequences. In the present disclosure, the horizontal pattern 510includes the sequence group 511 that includes three binary-codedsequences 513, 514, and 515, and the horizontal pattern 520 includes thesequence group 521 that includes three binary-coded sequences 523, 524,and 525. The binary-coded sequences 513, 514, and 515 may be arranged tobe sequentially adjacent in a column direction, and the otherbinary-coded sequences 523, 524, and 525 may also be arranged to besequentially adjacent in a column direction.

Each of the binary-coded sequences 513, 514, and 515 may includeaperiodic sequences that are repeatedly arranged. According to oneembodiment, the aperiodic sequences (or sub-sequences) that are includedin one of the binary-coded sequences 513, 514, and 515 may be differentfrom the aperiodic sequences (or sub-sequences) that are included inanother of the binary-coded sequences. For example, the number of bitsof each of the sub-sequences included in the binary-coded sequence 513may be different from the number of bits of each of the sub-sequencesincluded in the binary-coded sequence 514.

According to one embodiment, the horizontal pattern 510 may include ameta-sequence group 512 configured to separate the sequence group 511included in the horizontal pattern 510 from the sequence group 521included in another horizontal pattern 520. The meta-sequence group 512may include one or more meta-sequences, and the meta-sequence may beeasily distinguished from the binary-coded sequences included in thesequence groups 511 and 521.

According to one embodiment, the meta-sequence group 512 may include atleast one of a meta-sequence 516 formed of different binary codes thatare alternately repeated or a meta-sequence 517 formed of the samebinary code that is repeated. In this case, the meta-sequence 516 may bea reference to separate between bit patterns (for example, a bit pattern518 and a bit pattern 519) that represent binary codes constituting thebinary-coded sequences 513, 514, and 515. In addition, the meta-sequence517 may be a reference that is able to separate between the sequencegroups 511 and 521.

Here, if the filled bit pattern 518 may correspond to a binary code “1,”a blank bit pattern 519 may correspond to a binary code “0,” or viceversa.

According to one embodiment, each of the sequence groups 511 and 521 maybe created by splitting a single long sequence group. Therefore, thebinary-coded sequences located in the same row in the respectivesequence groups 511 and 521 may be sequences in which the same aperiodicsequence is repeatedly arranged. For example, the binary-coded sequence513 of the sequence group 511 and the binary-coded sequence 523 of thesequence group 521 may be sequences in which the same aperiodic sequenceis repeatedly arranged, and the binary-coded sequence 514 of thesequence group 511 and the binary-coded sequence 524 of the sequencegroup 521 may be sequences in which the same aperiodic sequence isrepeatedly arranged.

If the sequence group 511 includes two binary-coded sequences 513 and514; another sequence group 521 includes two binary-coded sequences 523and 524; and if the horizontal pattern 510 does not include themeta-sequence group 512, the binary-coded sequence 513 and thebinary-coded sequence 523 may be arranged to be spaced two rows apart ina column direction. This is similar to the situation in which themeta-sequence group 512 is configured with two rows that includes onlyblank bit patterns. Likewise, the binary-coded sequence 514 and thebinary-coded sequence 524 may also be arranged to be spaced two rowsapart in the column direction. Therefore, the binary-coded sequenceslocated in the same row in the adjacent sequence groups may be arrangedto be spaced at least two rows apart in the column direction. If thenumber of binary-coded sequences included in each sequence groupincreases or the meta-sequence group is included in the horizontalpattern, the binary-coded sequences located in the same row in theadjacent sequence groups may be arranged to be spaced three or more rowsapart.

According to one embodiment, the binary-coded sequence 513 may includebinary codes that are different from each other, and the binary codesmay be implemented in any shapes that are easily distinguished in thenaked eye, such as the bit pattern 518 and the bit pattern 519. Thedifferent binary codes may be the bit patterns 518 and 519 in arectangular shape as shown in FIG. 6, or may be implemented as a bitpattern in various forms including one of a circle, a rhombus, atriangle, a pentagon, etc.

According to some embodiments, when the capturing unit 330 of theoptical tracking system 300 captures an image of at least a part of thepattern 500 formed on the marker 310, the processor 350 may determinethe posture of the marker 310 based on the location of each sub-pattern(for example, some of the binary-coded sequences included in thesequence group), which is included in the pattern 500, in the entirepattern 500. For example, if the captured pattern image includes thepattern 500 as shown in FIG. 6, the processor 350 may identify thesub-pattern through a sequence window 610 in the sequence group 521. Thesize of the sequence window 610 may be equal to, or greater than, thesize of the sub-pattern.

The sub-pattern may be formed of a sequence block 611 that includes thesub-sequences of the respective binary-coded sequences 523, 524, and525. The processor 350 may use the sub-sequences included in thesequence block 611, and determine the location of the correspondingsub-pattern (or the sequence block 611) in the entire pattern 500, andmay determine the posture of the marker 310 based on the determinedlocation of the sub-pattern. According to one embodiment, the “sequenceblock” may have a size of j×1, where j may be the number of a pluralityof rows of binary-coded sequences (or parts thereof) included in thesequence block, and 1 may be the number of bits of the longestsub-sequence among the sub-sequences included in the sequence block.

According to one embodiment, each of the binary-coded sequences includedin the pattern 500 may include aperiodic sequences that are repeatedlyarranged, such as the PRBS, and the order (or the locations) of thesub-sequences in the respective aperiodic sequences may bepredetermined. For example, the processor 350 may extract the sequenceblock corresponding to the sub-pattern from the image of the capturedpattern 500, and may extract the sub-sequences, or some of them,constituting the PRBS in the sequence block in order to determine thelocation of the sub-pattern in the entire pattern 500 based on thelocation information of the extracted sub-sequence.

In some embodiments, the PRBSs having a length of 2n bits, which is tobe included in a pattern, may be created by using a shift register of nbits that has modulo-2 feedback. Each of sub-sequences of n bits in eachof the PRBSs created as described above may be arranged in apredetermined location in the PRBS. According to another embodiment, thePRBSs may be created by performing a repeated XOR-operation for an inputvalue and an output value of the shift register of n bits. According tosome other embodiments, the PRBSs may be created by using the Fibonaccilinear feedback shift register. However the method of creating thebinary-coded sequences that are included in the pattern used in thepresent disclosure is not limited to the PRBS creation method describedabove, and, for example, well-known methods, such as QRSS (Quasi-randomSequence signal), or various binary-coded sequence creation methodssimilar to the same may be applied to the present disclosure.

According to another embodiment, the pattern 500 may be formed by usingthe De Bruijn Sequence that is a kind of the PRBS. The De BruijnSequence may be generally expressed in the form of B(k,n). Here, kdenotes the size of a circuit sequence of predetermined alphabets, and ndenotes an order that may refer to the length (the number of bits) ofeach of the sub-sequences constituting the De Bruijn Sequence. All thesub-sequences constituting the De Bruijn Sequence have the same length(the same number of bits), but have different bit arrays from eachother. That is, each of the sub-sequences to form the De Bruijn Sequencemay have a unique bit array in the De Bruijn Sequence, and thus eachsub-sequence may appear only once in the De Bruijn Sequence. Accordingto such a characteristic, the De Bruijn Sequence may be an aperiodicsequence in which the sub-sequences included therein are notperiodically arranged. In addition, the order or location of each of thesub-sequences in the De Bruijn Sequence may be predetermined.

FIG. 7 is a diagram of a configuration of the De Bruijn Sequence inwhich a De Bruijn Sequence 710 is expressed as B(2,2) as an example. TheDe Bruijn Sequence 710 of B(2,2) may be expressed as {0, 0, 1, 1}. Inone embodiment, the De Bruijn Sequence 710 of B(2,2) may include, asbasic alphabets, binary codes “0” and “1” having a size of 2, and may beformed by sequentially arranging {0, 0}, {0, 1}, {1, 1}, and {1, 0},which are different sub-sequences having a length of 2.

As described above, the De Bruijn Sequence has a characteristic in whichthe order of each of the sub-sequences constituting the same ispredetermined according to a value of an attribute variable (k, n). Inthe case of the De Bruijn Sequence 710 of B(2,2), {0, 0} is the first,{0, 1} is the second, {1, 1} is the third, and {1, 0} is the fourth inthe sequence {0, 0, 1, 1}. Therefore, based on the respective values (orbit arrays) of the sub-sequences that are arranged in the De BruijnSequence, it may be determined where the sub-sequence is located in theDe Bruijn Sequence 710.

According to the configuration and characteristics of the De BruijnSequence described above, aperiodic sequences having a length of 2^(n)bits may be created by using the De Bruijn Sequence of n-th order, suchas B(2, n). Therefore, when any sub-sequence having a length of n bitsis obtained from the aperiodic sequences as formed above, the locationof the corresponding sub-sequence may be determined in the De BruijnSequence based on a value of the corresponding sub-sequence. When apattern of the marker 310 is formed by using such a De Bruijn Sequence,based on the sub-sequence having a length of n bits that has beenextracted from the captured pattern image, the location of thesub-pattern including the sub-sequence may be determined in the entirepattern.

Meanwhile, as shown in FIG. 8, in the case of the binary-coded sequence810 in which the same De Bruijn Sequence 811, 812, 813, or 814 isrepeatedly arranged, each of the De Bruijn Sequences 811, 812, 813, and814 that are repeatedly arranged includes sub-sequences of the samearray. Therefore, it is difficult to determine where the correspondingsub-sequence is positioned in the De Bruijn Sequences based on the valueof a sub-sequence that is extracted from such De Bruijn Sequences 811,812, 813, and 814. In this case, the location of the correspondingsub-sequence may be determined in the binary-coded sequence 810 only ifthe location of the De Bruijn Sequence including the correspondingsub-sequence is determined first in the binary-coded sequence 810.

Meanwhile, the binary-coded sequence that is used to form a pattern hasan enough length to form the pattern. The length of the binary-codedsequence may increase as the order n of the binary-coded sequenceincreases regardless of whether the binary-coded sequence is the DeBruijn Sequence or PRBS. In addition, as the order n of the binary-codedsequence increases, the length of each sub-sequence included in thesequence increases as well. For example, the De Bruijn Sequence of the21st order may have a length of 2²¹=2,097,152 bits, but the length ofeach sub-sequence included in the sequence is 21 bits. Therefore, whenthe longer De Bruijn Sequence is required to form a pattern, the orderof the sequence becomes more than 21, and the length of the sub-sequenceincluded in the sequence becomes more than 21 bits.

According to one embodiment, in the case of creating a sequence forforming a pattern by using a plurality of De Bruijn Sequences of whichthe orders are different from each other, a sequence that is long enoughto form the pattern may even be created by using the De Bruijn Sequenceof relatively low order. FIG. 9 shows an diagram in which a De BruijnSequence 911 of B(2,3)-1 and a De Bruijn Sequence 921 of B(2,2) are usedtogether in order to form a pattern, according to one embodiment. The DeBruijn Sequence 911 of B(2,3)-1 is a modified De Bruijn Sequence that iscreated by using the remaining sub-sequences except for the sub-sequence{0, 0, 0} that includes only “0” among the sub-sequences constitutingthe De Bruijn Sequence of B(2,3). In the case of the De Bruijn Sequence911 {0, 0, 1, 1, 1, 0, 1} of B(2,3)-1, seven sub-sequences {0, 0, 1},{0, 1, 1}, {1, 1, 1}, {1, 1, 0}, {1, 0, 1}, {0, 1, 0}, and {1, 0, 0} maybe arranged in predetermined locations in the sequence 911. Meanwhile,the De Bruijn Sequence 921 of B(2,2) has the same configuration as theDe Bruijn Sequence 710 that has been described with reference to theFIG. 7. The reason why the pattern is created by using a normal DeBruijn Sequence together with a modified De Bruijn Sequence instead ofonly by using normal De Bruijn Sequences will be described in moredetail below.

The De Bruijn Sequence 911 of B(2,3)-1 may have a length of 2³−1=7 bits,and sub-sequences of the sequence 911 may have a length of 3 bits,respectively. Thus, when considering only the De Bruijn Sequence 911 ofB(2,3)-1, the total length of the binary-coded sequence required forobtaining the location information of the sub-sequence is 7 bits, andthe sub-sequence may have a length of 3 bits. In addition, the De BruijnSequence 921 of B(2,2) may have a length of 2²=4 bits, and thesub-sequence having the location information may have a length of 2bits.

When binary-coded sequences 910 and 920 in which two De Bruijn Sequences911 and 921 that have the configuration described above are repeatedlyarranged, respectively, are combined in the column direction, a patternincluding two rows may be formed. In this pattern, the binary-codedsequences 910 and 920 of two rows may be repeated in a cycle of 7×4=28bits corresponding to the least common multiple of the lengths of the DeBruijn Sequences 911 and 921. In this case, {0, 0, 1, 1, 1, 0, 1} thatis the De Bruijn Sequence 911 of B(2,3)-1 may be repeated four times,and {0, 0, 1, 1} that is the De Bruijn Sequence 921 of B(2,2) may berepeated seven times in the binary-coded sequences 910 and 920 of tworows that have a cycle of 28 bits. Therefore, when the De BruijnSequences of two rows are combined to then form a pattern, the length inwhich the pattern has an aperiodic characteristic may be greater thanthe length in which the combined De Bruijn Sequences 911 and 921 have anaperiodic characteristic.

In the binary-coded sequences 910 and 920 that are combined as describedabove, a sequence window 930 may be placed in a certain location of thebinary-coded sequences 910 and 920, which has a size of 2×3, wherein thenumber of columns corresponds to the number of bits (i.e., 3) of thelongest sub-sequence among the sub-sequences of two De Bruijn Sequences911 and 921 and the number of rows corresponds to the number of combinedsequences (i.e., 2) so that a sequence block may be extracted throughthe sequence window 930. The location of the sequence block in thebinary-coded sequences 910 and 920 may be determined by using thesub-sequences {0, 0, 1} and {1, 1} that are in the leftmost location inthe sequence block.

In the present disclosure, the size of a pattern region that is to becaptured by the capturing unit 330 for the tracking of the marker 310may be determined according to the number of bits of the columns androws of the sequence window. For example, in the embodiment of FIG. 9,the sequence block may be extracted from the captured pattern regionthrough the sequence window 930 in a size of 2×3, and the location ofthe extracted sequence block may be determined in the sequences 910 and920 having a length of 28 bits.

On the contrary, likewise, a sequence (or pattern) having a length of 28bits may be created by using the De Bruijn Sequence of the fifth order{for example, a single B(2,5)}, but, in this case, the length of thesub-sequence included in the pattern becomes 5 bits.

Therefore, compared with the case where a pattern is created by using asingle De Bruijn Sequence of the same length, in the case where apattern is created by using the combined De Bruijn Sequences 910 and 920of the same length as shown in the embodiment of the present disclosure,the size of the sequence window for identifying the sub-sequenceincluded in the sequence block may be significantly reduced.

This means that the conditions for the size of a region that is requiredfor the capturing unit 330 to accurately capture an image for trackingthe marker 310 may be relaxed and the possibility in which the processor350 successfully identifies every moment the sub-sequence from thecaptured region in the pattern image may be considerably improved.

For example, in the embodiment of FIG. 9, if bit patterns of 3 bits inthe horizontal and 2 bits in the vertical are accurately identified inat least one portion of the captured pattern image, the location of thesequence block including sub-sequences corresponding to thecorresponding bit patterns may be determined in the pattern. On thecontrary, in the case of using the De Bruijn Sequence of the fifthorder, only if the bit patterns of 5 bits in the horizontal areaccurately identified in at least one portion of the captured patternimage, the location of the sequence block including sub-sequencescorresponding to the corresponding bit patterns may be determined in thepattern.

In order to determine a more precise location, for example, when using apattern of the combined De Bruijn Sequences B(2,7)-1, B(2,6), B(2,5)-1,B(2,4)-1, and B(2,3)-1, if only bit patterns of 7 bits in the horizontal(the length of the sub-sequence) and 5 bits in the vertical (the numberof the De Bruijn Sequences) {when considering meta-sequences, bitpatterns of 7 bits in the horizontal and 7 bits in the vertical (a sumof the number of the De Bruijn Sequences and the number ofmeta-sequences)} are accurately identified in at least one portion ofthe captured pattern image, the location of the sequence block includingsub-sequences corresponding to the corresponding bit patterns may bedetermined in the pattern. On the contrary, in the case of using the DeBruijn Sequence of the 25th order of the same length, only if all bitpatterns of 25 bits in the horizontal are accurately identified in atleast one portion of the captured pattern image, the location of thesub-sequence corresponding to the corresponding bit patterns may bedetermined in the pattern.

Meanwhile, the captured image may have a distortion caused by a relativemoving speed, rotating, and tilting of the marker and the capturingunit, a distortion cause by the characteristics of the optical system, adistortion caused by thermal noise, vibration, and read-out propertiesof the image sensor, or the like. Thus, as the length of the sequencewindow increases in one direction, the possibility in which all the bitpatterns that are extracted through the sequence window are accuratelyidentified may decrease. In the example above, the sequence window of 7bits in the horizontal and 5 bits in the vertical is almost always moreadvantageous than a sequence window of 25 bits in the horizontal and 1bit in the vertical.

Meanwhile, as shown in the embodiment described with reference to FIG.9, some of the De Bruijn Sequences constituting the combinedbinary-coded sequences may be the modified De Bruijn Sequences, exceptfor the sub-sequence that includes only “0.” It is due to the fact thatthe repetition cycle of the combined binary-coded sequences becomes aleast common multiple of the lengths (the number of bits) of the DeBruijn Sequences. Therefore, if the least common multiple of the lengthsof the De Bruijn Sequences is increased by: (i) increasing the number ofbinary-coded sequences to be combined to form a pattern; (ii) settingthe orders of the De Bruijn Sequences constituting the binary-codedsequence to be different from each other; or (iii) properly excludingthe sub-sequence that includes only “0” from the De Bruijn Sequencesconstituting the binary-coded sequence, the longer combined binary-codedsequences may be created. As described above, the number of the DeBruijn Sequences to be combined to form a pattern, the order of each DeBruijn Sequence, and the exclusion of the sub-sequence that includesonly “0” from the De Bruijn Sequences may be appropriately selectedaccording to the length of the combined binary-coded sequence, which isrequired to form the pattern.

For example, it is assumed that a pattern is formed by using five DeBruijn Sequences and the De Bruijn Sequences are B(2,7)-1, B(2,6),B(2,5)-1, B(2,4)-1, and B(2,3)-1. As a result, the total length of thecombined binary-coded sequence that has an aperiodic characteristic maybe (2⁷−1)×(2⁶)×(2⁵−1)×(2⁴−1)×(2³−1)=26,456,640 bits. This length may beobtained only if the De Bruijn Sequence of at least the 25th order isused. If the sub-sequence that includes only “0” is not excluded fromthe De Bruijn Sequence of B(2,5), the total length of the aperiodicsequence may decrease to (2⁷−1)×(2⁵)×(2⁴−1)×(2³−1)=426,720 bits. This ismerely a length of pattern that can be obtained by using the De BruijnSequence of the 19th order.

FIG. 10 depicts a diagram showing a method for implementing atwo-dimensional pattern by using a single long horizontal pattern thatis formed by combining a plurality of rows of binary-coded sequences,according to one embodiment of the present disclosure. According to oneembodiment, a single long horizontal pattern may be divided into severalpatterns having a smaller length, and then, the divided patterns may bearranged in a plurality of rows in order to thereby implement atwo-dimensional pattern 1010. According to another embodiment, a singlelong horizontal pattern may be divided into several patterns having asmaller length, and then, the divided patterns may be arranged in aplurality of rows in order to thereby implement another two-dimensionalpattern 1030. Thereafter, a new two-dimensional pattern may beimplemented by sequentially combining the two-dimensional patterns 1010and 1030.

According to one embodiment, when dividing a single horizontal patternto then create a two-dimensional pattern, the whole or a part of thehorizontal pattern may be used. For example, a horizontal pattern of1,000 bits long may be divided into 10 patterns having a length of 100bits, and then, the 10 patterns may be arranged in a plurality of rowsso that a two-dimensional pattern may be implemented. As anotherexample, the two-dimensional pattern may also be implemented by dividingonly 800 bits of the horizontal pattern of 1000 bits long. In addition,10 markers that have different patterns from each other may be made bydividing the horizontal pattern of 1000 bits long into 10 horizontalpatterns of 100 bits long and forming the 10 divided horizontal patterns(or sequence) on the 10 markers, respectively.

According to one embodiment, when a plurality of patterns are made,which are to be used for a plurality of markers, by dividing a singlehorizontal pattern as described above, the sequence block itself that isextracted from each of the divided patterns through a sequence windowmay be used as the ID of the corresponding marker. For example, ahorizontal pattern is assumed, which has 1,000 sequence blocks that areidentified through a sequence window. When the horizontal pattern isdivided into 10 small patterns that include 100 sequence blocks and the10 divided small patterns are used as the patterns for 10 markers,respectively, the marker may be predetermined so that the patternincludes 1,000 sequence blocks among the 10 markers. For example, thefirst marker may be predetermined to include the first to 100th sequenceblocks, and the second marker may be predetermined to include the 101stto 200th sequence blocks. Likewise, the sequence blocks to be includedin the remaining third to tenth markers may be predetermined.

Therefore, based on such information, the processor 350 may determine anID of the marker that is currently tracked only by determining thelocation information of the sequence block that is extracted fortracking among the 1,000 sequence blocks. In the example above, if theprocessor 350 determines that the extracted sequence block correspondsto the 120th sequence block, the processor 350 may recognize that themarker corresponds to the second marker. That is, even if the pattern ofthe marker does not include a separate pattern or code information toprovide the ID of the marker, the processor 350 may distinguish thecorresponding marker from other markers based on the locationinformation of the sequence block, which is extracted from the patternof the marker.

With regard to the marker 310, according to one embodiment of thepresent disclosure, as described above, the pattern information may beidentified through the optical system 312, such as lenses, from theoutside of the marker 310 by installing a light source inside or outsidethe marker 310 and by allowing the light from the light source to bereflected by, or pass through, the pattern plane 311 on which a patternis formed. The pattern plane 311 on which a pattern is formed may beimplemented by using a material having a high or low reflectivity forthe light in order to reflect or transmit the light from the lightsource. Here, the “reflectivity” may refer to a ratio of the energy ofthe light incident on the pattern plane to the energy of the light thatis reflected by the pattern plane.

According to one embodiment, in the case of implementing the pattern byusing the binary-coded sequences, the portions where different binarycodes, such as “0” or “1,” are implemented on the pattern plane may beformed of materials having different reflectivities for the light,respectively. When the pattern implemented on the pattern plane, whichis formed as described above, is captured by the capturing unit 330, theamount of the light transferred to the capturing unit 330 varies with“0” or “1” constituting the pattern so that “0” and “1” may beseparately identified in the pattern image. According to anotherembodiment, the portions that represent “0” or “1” in the pattern may beformed in different images or shapes. For example, an image representing“0” in the pattern may be expressed as a circle, and an imagerepresenting “1” may be expressed as a rectangle. However, the methodfor expressing the binary-coded sequences or the binary codes includedin the sequences on the pattern is not limited thereto, and they may beimplemented in other various images or shapes.

According to one embodiment, the marker 310 may include an opticalsystem 312, such as lenses, to allow at least a part of the pattern tobe visually identified from the outside of the marker 310. The patternplane 311 may be disposed inside the marker 310 in order for the patternto be transferred to the outside of the marker 310 in the form of aparallel outgoing light through the optical system 312. In the casewhere the pattern plane 311 is disposed inside the marker 310 asdescribed above, the optical system of the marker 310 may be combinedwith the optical system of the capturing unit 330 of the opticaltracking system 300 in order to thereby configure an infinite opticalsystem. The capturing unit 330 of the optical tracking system 300 mayobtain a pattern image of the pattern, which is enlarged through theinfinite optical system. Therefore, in the case of the infinite opticalsystem that is configured as described above, even if the marker 310 islocated far away from the capturing unit 330, at least a part of thepattern can be identified from the pattern image that is captured by thecapturing unit 330.

According to one embodiment, in order for the pattern to be transferredto the outside of the marker 310 in the form of a parallel outgoinglight, the pattern may be implemented in a portion of the pattern plane311 where the focal point of the lens constituting the optical system312 is formed. According to one embodiment, the pattern plane 311 onwhich a pattern is formed may have a flat or curved surface. In thiscase, the lens constituting the optical system 312 may be designed suchthat the focal point of the lens may be formed on the flat or curvedsurface of the pattern plane 311. For example, if the optical system 312is designed by using a fisheye lens, the focal point of the lens may beformed on the flat or curved surface of the pattern plane 311.

<Capturing Unit>

As described with reference to FIG. 3 above, in order to capture animage of a pattern for tracking the marker 310, the capturing unit 330may include two or more capturing elements 332 and 334, and lenses 331and 333 corresponding to the same. At least a part of the pattern, whichcan be identified from the outside of the marker 310, may be captured bythe capturing elements 332 and 334 through the lens 331 and the lens333.

In the capturing unit 330, according to one embodiment of the presentdisclosure, the capturing elements 332 and 334 may be installed to befixed in the focal lengths of the lenses 331 and 333 corresponding tothe capturing elements 332 and 334, respectively. As a result, thecapturing elements 332 and 334 may be positioned at the afocal pointthat is the focal point of the optical system that is configured bycombining the optical system 312 of the marker 310 and the lenses 331and 333 of the capturing unit 330, respectively. In this case, thecapturing elements 332 and 334 may capture an enlarged image for thewhole or a part of the pattern that is formed on the marker 310regardless of a change in distance from the marker depending on themovement of the marker 310. In addition, the capturing unit 330 maycapture an image of the pattern without focusing, even if the marker 310is moved.

In one embodiment, the capturing elements 332 and 334 may be disposed tohave a proper angle or direction in the capturing unit 330 in order toobtain a pattern image for the same region of a pattern that is formedon the marker 310.

Likewise, in the case where the optical tracking system 400 includes twocapturing units 430 and 440 as shown in FIG. 4, the capturing elements432 and 442 that are included in the capturing units 430 and 440,respectively, may be installed to be fixed in the focal lengths of thecorresponding lenses 431 and 441. In addition, the capturing elements430 and 440 may be disposed to have a proper angle or direction in theoptical tracking system 400 in order to obtain a pattern image for thesame region of a pattern that is formed on the marker 310.

Meanwhile, when at least a part of the pattern is captured as a patternimage by the capturing element in the outside of the marker 310, thesize of the region where at least a part of the pattern is captured onthe pattern image may vary with at least one of the distances from thelocation (for example, the location of the capturing unit), where thepattern image is captured, to the marker 310 and the location of themarker 310, respectively.

<Processor>

The optical tracking system 300, according to one embodiment of thepresent disclosure, may include a processor 350 that is able tocalculate the location and the posture of the marker 310 based on theinformation that is extracted from at least a part of the patternincluded in the pattern image that is obtained by the capturing unit330.

In some embodiments, the processor 350 may extract the size of thepattern region and the central coordinates of the pattern region fromthe captured pattern image, and may determine the location of the marker310 based on the same. For example, in the case where the shape andaperture of the optical system that are formed by the marker 310 and thecapturing unit 330 are circles, the pattern region in the pattern imagemay be shown in an approximately circular shape or in a part of thecircular shape as shown in FIG. 11. The size of the circular shaperepresenting the pattern region on the pattern image may vary with thedistance from the capturing unit 330 to the marker 310 or with thelocation of the marker 310. The processor 350 may extract the diameterand central coordinates of a circle that represents the pattern regionon the pattern image, and may compare the same with the diameter andfocal length of the lens corresponding to the capturing element of thecapturing unit 330 in order to thereby obtain coordinate valuescorresponding to the location of the marker 310 in the three-dimensionalspace with a central point of the lens as the origin. In this case, whena plurality of lenses is implemented to correspond to the capturingelement, the plurality of lenses may be defined as a single thin lensaccording to the well-known thin lens theory. Accordingly, the diameter,the focal length, and the central point of the lens corresponding to thecapturing element of the capturing unit 330 may be expressed as thediameter, the focal length, and the central point of a single thin lens,respectively, which is defined as described above.

According to another embodiment, the processor may determine thelocation of the marker 310 by using triangulation. The processors 350and 450 may extract the central coordinates of the pattern regions (forexample, the central coordinates of the circular shape in FIG. 11) fromthe pattern images that are captured by the capturing elements 332 and334 or the capturing units 430 and 440 that are placed in differentlocations, and may calculate the location of the marker 310 by usingtriangulation based on the central coordinates. For example, theprocessor 350 and 450 may calculate the location of the marker 310 byusing the central coordinates of the pattern region on each patternimage and by using a geometric relationship between the directions inwhich the capturing elements 332 and 334 or the capturing units 430 and440 view the marker 310. In this case, the capturing elements 332 and334 or the capturing unit 430 and 440 are placed in different locations.

According to another embodiment, the processor 350 may determine thelocations of two markers by using pattern images for the two markersthat have a predetermined geometric relationship. For example, when thecapturing unit captures pattern images of patterns that are formed ontwo markers, the processor 350 may determine the locations of the twomarkers based on a geometric relationship between the two markers andbased on a relationship between the location of at least a part of thepattern on the pattern image and the location of at least a part of thepattern on each marker. In this case, the distance between the patternsthat are formed on the two markers may be determined from the geometricrelationship between the two markers. The processor 350 may determinethe locations of the two markers based on the location relationshipabove by using the central coordinates of the pattern on each marker.

A method for determining the location of the marker 310 by the processor350 may be conducted by properly selecting one of the well-knownalgorithms, and one example thereof is disclosed in Korean Patent No.10-1406220.

According to one embodiment, the processor 350 may determine the postureof the marker 310 based on a location change of at least a part (forexample, the sub-pattern) of the pattern on the pattern image. Theprocessor 350 may obtain a posture matrix R that represents the postureof the marker 310 by using Equation 1 based on such a principle.

$\begin{matrix}{{s\begin{bmatrix}u_{i}^{\prime} \\v_{i}^{\prime} \\1\end{bmatrix}} = {{{{\lbrack A\rbrack\lbrack R\rbrack}\lbrack C\rbrack}\begin{bmatrix}u_{i} \\v_{i} \\1\end{bmatrix}} = {\quad{{{\begin{bmatrix}{- \frac{f_{c}}{{pw}.}} & 0 & u_{c}^{\prime} \\0 & {- \frac{f_{c}}{{ph}.}} & v_{c}^{\prime} \\0 & 0 & 1\end{bmatrix}\begin{bmatrix}r_{11} & r_{12} & r_{13} \\r_{21} & r_{22} & r_{23} \\r_{31} & r_{32} & r_{33}\end{bmatrix}}\begin{bmatrix}1 & 0 & {- u_{c}} \\0 & 1 & {- v_{c}} \\0 & 0 & f_{b}\end{bmatrix}}\begin{bmatrix}u_{i} \\v_{i} \\1\end{bmatrix}}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1,

=r₃₁u_(i)+r₃₂v_(i)+r₃₃f_(b); u′_(i), v′_(i) denotes the pixelcoordinates of the i-th sub-pattern on the pattern image; u_(i), v_(i)denotes the coordinates of the i-th sub-pattern on the pattern; u_(c),v_(c) denotes the actual coordinates of the central point of thepattern; pw denotes a pixel area of the pattern image; ph denotes apixel height of the pattern image; f_(c) denotes a focal length of thelens corresponding to the capturing element; and f_(b) denotes a focallength of the lens of the marker.

In order to execute a calculation according to Equation 1, the processor350 may extract the location of each sub-pattern (for example, thecoordinates of the i-th sub-pattern on the pattern in Equation 1) in thepattern from the pattern image. The pattern, according to one embodimentof the present disclosure, may be formed by using the binary-codedsequences that are formed by the De Bruijn Sequences that are repeatedlyarranged. The processor 350 may extract, through a sequence window, oneor more sequence blocks constituting the sub-patterns from the patternimage including the whole or a part of the pattern that is formed asdescribed above, and may determine the location (coordinates) of thesequence block on the pattern by using the sub-sequences included in thesequence block.

Hereinafter, a method in which the processor 350 determines the locationof each sub-pattern from the pattern image of the pattern that is formedby using the De Bruijn Sequences will be described in detail.

First, in order to extract the information for tracking the marker fromthe pattern image, the processor 350 may read binary-coded sequencesfrom the pattern image. Next, the processor 350 may extract one or moresequence blocks constituting the sub-pattern from the read binary-codedsequences, and may calculate the location (coordinates) of eachsub-pattern in the whole pattern by using the sub-sequences included ineach sequence block.

According to one embodiment, the processor 350, as shown in FIG. 11,may: i) extract a single sequence block 1130 through the sequence window1120 from the pattern 1110 that is formed by using the De BruijnSequences; and ii) obtain the location of the sub-pattern that includesone sequence block 1130 based on the sub-sequences included in the same.For example, a simultaneous equation for obtaining the locationinformation of one sequence block 1130 may be derived by using acharacteristic in which the sub-sequences imply the location informationon the De Bruijn Sequence and by using a characteristic in which all thelengths between the start bits of the binary-coded sequences and thestart bit of the sequence block 1130 are the same in the binary-codedsequences. The processor 350, based on the values of the simultaneousequation, may calculate the location of the sub-pattern including asingle sequence block 1130 in the whole pattern, and may determine theposture of the marker 310 based on the same.

The processor 350 may calculate the posture of the marker 310 based ononly a single sequence block as described above. If a plurality ofsequence blocks is extracted, the processor 350 may calculate aplurality of postures of the marker 310 by using all or some of theplurality of sequence blocks extracted from the pattern image, and maydetermine the posture of the marker 310 through a statistical operationof the calculation result. In this case, the statistical operation mayrefer to an operation for obtaining an average, a median value, or amode value, but it is not limited thereto.

<Method for Tracking Marker>

FIG. 12 is a flowchart of a method for tracking a marker on which apattern is formed in an optical tracking system, according to oneembodiment of the invention. Hereinafter, a method for tracking themarker 310 will be described in more detail in relation to eachoperation with reference to the drawing.

First, in operation S1210, one or more capturing elements that areincluded in one or more capturing units may obtain a pattern image forat least a part of a pattern. For example, referring to FIG. 4, thecapturing elements 432 and 442 included in the capturing units 430 and440, respectively, may capture the pattern image for at least a part ofthe pattern, which can be visually identified from the outside of themarker 310 through the optical system 312, based on the focal lengths ofthe lenses 431 and 441 corresponding to the capturing elements 432 and442, respectively. In this case, if the pattern is implemented on thepattern plane 311 on which the focal point of the optical system 312 isformed, the optical tracking system 400 may form an infinite opticalsystem. The capturing units 430 and 440 may capture an enlarged image ofat least a part of the pattern, as the pattern image, through theinfinite optical system, respectively.

The pattern, according to one embodiment of the present disclosure, mayinclude a plurality of rows of binary-coded sequences. The binary-codedsequence of each row may include aperiodic sequences that are repeatedlyarranged, such as a De Bruijn Sequence. In this case, each of theaperiodic sequences constituting a plurality of rows of binary-codedsequences may include a plurality of sub-sequences that are arranged ina predetermined order.

According to one embodiment, the aperiodic sequences that are includedin one of the plurality of rows of binary-coded sequences may bedifferent from the aperiodic sequences that are included in another ofthe plurality of rows of binary-coded sequences. For example, the numberof bits in each sub-sequence included in the binary-coded sequence inone row may be different from the number of bits in each sub-sequenceincluded in the binary-coded sequence in another row. The number of bitsof the sub-sequence in the De Bruijn Sequence may be determinedaccording to the order of the De Bruijn Sequence. The detailedconfiguration of the pattern of the embodiments above has been describedbefore, which will be omitted here.

When the pattern image is obtained through operation S1210, theprocessor may process the information that is extracted from at least apart of the pattern that is included in the pattern image in order tothereby track the location and the posture of the marker in operationS1220. For example, referring to FIG. 4, the processor 450 may processthe information extracted from at least a part of the pattern that isincluded in the pattern image that is obtained by the capturing elements432 and 442 in order to thereby track the location and the posture ofthe marker 310.

In one embodiment, the method for tracking the location and the postureof the marker 310, which is executed in operation S1220, will bedescribed in detail with reference to FIG. 13. First, in operationS1221, the processor may determine the location of the marker based ontriangulation by using pattern images obtained by two or more capturingunits or two or more capturing elements. For example, referring to FIG.3, the processor 350 may determine the location of the marker 310 byusing triangulation based on the pattern images that are obtained by thecapturing elements 332 and 334 that are placed in different locations.In addition, referring to FIG. 4, the processor 450 may determine thelocation of the marker 310 by using triangulation based on the patternimages that are obtained by the capturing units 430 and 440 that areplaced in different locations.

According to one embodiment, the processors 350 and 450 may determinethe location of the marker 310 based on triangulation by using thecentral coordinates of the pattern region (for example, the centralcoordinates of a circle in FIG. 11) on each pattern image and ageometric relationship between the directions in which the capturingunits 430 and 440 or the capturing elements 332 and 334 view the marker310. Although the location of the marker is determined by usingtriangulation in the embodiments above, it is not limited thereto, andother location determining methods rather than triangulation may beused. In this case, operation S1221 may be omitted.

In operation S1222, the processor may extract one or more sequenceblocks from the pattern images. For example, referring to FIGS. 3 and 6,the processor 350 may extract, through the sequence window 610 having apredetermined size, at least one sequence block 611 from the patternimage that is obtained by the capturing unit 330. The sequence block 611may include some of a plurality of rows of binary-coded sequencesconstituting the pattern.

According to one embodiment, the sequence block may include asub-sequence that corresponds to each of the plurality of rows ofbinary-coded sequences. The sequence block may have a size of j×1,wherein j may be the number of binary-coded sequences that are includedin the sequence block, and 1 may be the number of bits of the longestsub-sequence among the sub-sequences included in the sequence block.

When one or more sequence blocks are extracted as described above, inoperation S1223, the processor may determine the posture of the markerbased on the one or more extracted sequence blocks. In some embodiments,first, the processor may determine the location of the sub-pattern inthe pattern, which is represented by the sequence block, based on thesub-sequences included in each of a plurality of rows of binary-codedsequences that are included in the sequence block. Thereafter, theprocessor may determine the posture of the marker based on thedetermined location of the sub-pattern in the pattern. For example,referring to FIGS. 5 and 6, the processor 350 may determine the locationof the sub-pattern in the whole pattern 500, which is formed by thesequence block 611, by using the sub-sequences that are included in theextracted sequence block 611. The processor 350 may determine theposture of the marker 310 based on the determined location of thesub-pattern in the whole pattern 500.

In the embodiment described with reference to FIG. 13, the processordetermines the posture of the marker 310 after determining the locationof the marker. In another embodiment, the processor may determine theposture of the marker prior to determining the location of the marker.In some embodiments, the processor may determine the location and theposture of the marker by processing the same in parallel.

Although the method has been described through specific embodiments, themethod may also be embodied as computer-readable codes in acomputer-readable recording medium. The computer-readable recordingmedium includes all kinds of recording devices that store data that canbe read by a computer system. The examples of the computer-readablerecording medium may include ROM, RAM, CD-ROM, magnetic tapes, floppydisks, optical data storage devices, or the like, or may be implementedin the form of a carrier wave (for example, the transmission through theInternet). In addition, the computer-readable recording medium may bedistributed to computer systems that are connected through a network,and a computer-readable code may be stored and executed in a distributedmanner. In addition, functional programs, codes, and code segments forimplementing the embodiments above may be easily inferred by theprogrammers who are skilled in the art.

Although the present disclosure has been described in relation to someembodiments in the present specification, it should be noted that theremay be various modifications and changes without departing from thespirit and scope of the present disclosure, which can be understood bythose skilled in the art. In addition, such modifications and changesshould be construed to belong to the scope of the claims appendedherein.

What is claimed is:
 1. A marker with a pattern formed thereon,comprising: an optical system, wherein: at least a part of the patternthat uniquely appears depending on a direction in which the pattern isviewed from an outside of the marker through the optical system, isvisually identified from the outside of the marker; the pattern includesa plurality of rows of binary-coded sequences; the binary-coded sequenceof each of the plurality of rows includes aperiodic sequences that arerepeatedly arranged; the aperiodic sequences included in thebinary-coded sequence of one row of the plurality of rows are differentfrom the aperiodic sequences included in the binary-coded sequence ofanother row of the plurality of rows; and each of the aperiodicsequences includes a plurality of sub-sequences that are arranged in apredetermined order.
 2. The marker according to claim 1, wherein theplurality of rows of binary-coded sequences include a first binary-codedsequence and a second binary-coded sequence that are adjacent in acolumn direction, and wherein a number of bits of each of thesub-sequences included in the first binary-coded sequence is differentfrom a number of bits of each of the sub-sequences included in thesecond binary-coded sequence.
 3. The marker according to claim 2,wherein the pattern further include a third binary-coded sequencepositioned in a m-th row from the first binary-coded sequence in thecolumn direction and a fourth binary-coded sequence positioned in them-th row from the second binary-coded sequence in the column direction,wherein the aperiodic sequence included in the third binary-codedsequence is equal to the aperiodic sequence included in the firstbinary-coded sequence, and the aperiodic sequence included in the fourthbinary-coded sequence is equal to the aperiodic sequence included in thesecond binary-coded sequence, and wherein m is a natural number of 2 ormore.
 4. The marker according to claim 3, wherein the pattern includes:a first sequence group including the first and second binary-codedsequences; a second sequence group including the third and fourthbinary-coded sequences; and a meta-sequence configured to separate thefirst and second sequence groups from each other.
 5. The markeraccording to claim 4, wherein the meta-sequence is different from thebinary-coded sequences that are included in the first and secondsequence groups.
 6. The marker according to claim 5, wherein themeta-sequence is a sequence in which different binary codes arealternately repeated, or is comprised of only the same binary code. 7.The marker according to claim 1, further comprising a pattern plane onwhich the pattern is formed, wherein different binary codes that areincluded in the binary-coded sequences of the pattern formed on thepattern plane are made of materials that have different reflectivitiesfrom each other.
 8. The marker according to claim 1, further comprisinga pattern plane on which the pattern is formed, wherein the opticalsystem includes a lens, and the pattern is formed in a portion where afocal point of the lens is formed on the pattern plane.
 9. The markeraccording to claim 8, wherein the pattern plane has a flat or curvedsurface, and the lens allows the focal point to be formed on the flat orcurved surface.
 10. The marker according to claim 1, wherein theaperiodic sequence is a PRBS (Pseudo-Random Binary Sequence) or DeBruijn Sequence.
 11. The marker according to claim 1, wherein if atleast a part of the pattern is captured as a pattern image in theoutside of the marker, a size of a region where at least a part of thepattern is captured on the pattern image varies with at least one of adistance from a location in which the pattern image is captured to themarker or a location of the marker.
 12. An optical tracking systemcomprising: one or more markers on which a pattern is formed; one ormore capturing units configured to include one or more capturingelements that obtains a pattern image of the pattern; and a processorconfigured to track locations and postures of the one or more markersbased on information that is extracted from at least a part of thepattern included in the pattern image, wherein: the pattern includes aplurality of rows of binary-coded sequences; the binary-coded sequenceof each of the plurality of rows includes aperiodic sequences that arerepeatedly arranged; the aperiodic sequences included in thebinary-coded sequence of one row of the plurality of rows are differentfrom the aperiodic sequences included in the binary-coded sequence ofanother row of the plurality of rows; and each of the aperiodicsequences includes a plurality of sub-sequences that are arranged in apredetermined order.
 13. The optical tracking system according to claim12, wherein the optical tracking system extracts one or more sequenceblocks from the pattern image and then tracks the one or more markers,and wherein the one or more sequence blocks include a part of theplurality of rows of binary-coded sequences.
 14. The optical trackingsystem according to claim 13, wherein the one or more sequence blockshave a size of j×1 in which j denotes a number of binary-coded sequencesthat are included in the one or more sequence blocks and 1 denotes anumber of bits of a longest sub-sequence among the plurality ofsub-sequences included in the one or more sequence blocks.
 15. Theoptical tracking system according to claim 13, wherein the processordetermines postures or IDs of the one or more markers based on the oneor more sequence blocks.
 16. The optical tracking system according toclaim 15, wherein the part of the plurality of rows of binary-codedsequences are sub-sequences that are included in each of the pluralityof rows of binary-coded sequences, and wherein the processor determinesa location of a sub-pattern represented by the one or more sequenceblocks in the pattern based on the sub-sequences, and determines thepostures of the one or more markers based on the location of thesub-pattern.
 17. The optical tracking system according to claim 15,wherein the part of the plurality of rows of binary-coded sequences aresub-sequences that are included in each of the plurality of rows ofbinary-coded sequences, and wherein the processor determines locationinformation on the one or more sequence blocks in the plurality ofbinary-coded sequences based on the sub-sequences, and determines theIDs of the one or more markers based on the location information. 18.The optical tracking system according to claim 12, wherein the one ormore capturing units include two or more capturing units, or the one ormore capturing elements include two or more capturing elements, andwherein the processor determines the locations of the one or moremarkers based on triangulation by using pattern images that are obtainedby the two or more capturing units or by the two or more capturingelements.
 19. The optical tracking system according to claim 18, whereinthe processor determines the locations of the one or more markers basedon central coordinates of a region of the pattern on each of the patternimages and triangulation by using a geometric relationship betweendirections in which the two or more capturing units or the two or morecapturing elements view the one or more markers.
 20. The opticaltracking system according to claim 12, wherein the processor determinesthe locations of the one or more markers based on a size of a region ofthe pattern and central coordinates of the pattern region, on thepattern image obtained by the one or more capturing units.
 21. Theoptical tracking system according to claim 12, wherein the one or moremarkers include two markers that has a predetermined geometricrelationship, wherein the capturing units capture pattern images ofpatterns that are formed on the two markers, respectively, and whereinthe processor determines the locations of the two markers based on thepredetermined geometric relationship and a relationship between alocation of at least a part of the patterns on the pattern images and alocation of at least a part of the pattern on each of the markers. 22.The optical tracking system according to claim 12, wherein the pluralityof rows of binary-coded sequences include a first binary-coded sequenceand a second binary-coded sequence that are adjacent in a columndirection, and wherein a number of bits of each sub-sequence included inthe first binary-coded sequence is different from a number of bits ofeach sub-sequence included in the second binary-coded sequence.
 23. Theoptical tracking system according to claim 22, wherein the patternfurther includes a third binary-coded sequence positioned in a m-th rowfrom the first binary-coded sequence in the column direction and afourth binary-coded sequence positioned in the m-th row from the secondbinary-coded sequence in the column direction, wherein the aperiodicsequence included in the third binary-coded sequence is equal to theaperiodic sequence included in the first binary-coded sequence, and theaperiodic sequence included in the fourth binary-coded sequence is equalto the aperiodic sequence included in the second binary-coded sequence,and wherein m is a natural number of 2 or more.
 24. The optical trackingsystem according to claim 12, wherein the one or more markers include afirst lens, wherein the pattern is implemented on a pattern plane onwhich a focal point of the first lens is formed, and wherein the one ormore capturing units include a second lens that is configured such thatat least a part of the pattern, which is visually identified from theone or more markers in a direction in which the capturing units view theone or more markers through the first lens, is captured on the one ormore capturing elements, and obtains a pattern image of at least a partof the pattern in a focal length of the second lens.
 25. The opticaltracking system according to claim 24, further comprising a light sourceconfigured to emit light onto the one or more markers in order toenhance the light incident on the second lens through the first lenswith respect to at least a part of the pattern.
 26. An optical trackingmethod for tracking a marker on which a pattern is formed, the methodcomprising: obtaining, by one or more capturing elements included in oneor more capturing units, a pattern image of at least a part of thepattern; and proceeding, by a processor, information extracted from atleast a part of the pattern included in the pattern image and tracking alocation and a posture of the marker, wherein: the pattern includes aplurality of rows of binary-coded sequences; the binary-coded sequenceof each of the plurality of rows includes aperiodic sequences that arerepeatedly arranged; the aperiodic sequences included in thebinary-coded sequence of one row of the plurality of rows are differentfrom the aperiodic sequences included in the binary-coded sequence ofanother row of the plurality of rows; and each of the aperiodicsequences includes a plurality of sub-sequences that are arranged in apredetermined order.
 27. The method according to claim 26, wherein thetracking the location and the posture of the marker comprises extractingone or more sequence blocks from the pattern image, and wherein the oneor more sequence blocks have a size of j×1 in which j denotes a numberof binary-coded sequences that are included in the one or more sequenceblocks and 1 denotes a number of bits of a longest sub-sequence amongthe sub-sequences included in the one or more sequence blocks.
 28. Themethod according to claim 27, wherein the tracking the location and theposture of the marker comprises determining the posture of the markerbased on the one or more extracted sequence blocks.
 29. The methodaccording to claim 28, wherein the determining the posture of the markercomprises: determining a location of a sub-pattern represented by theone or more sequence blocks in the pattern based on the sub-sequencesthat are included in each of the plurality of rows of binary-codedsequences that are included in the one or more sequence blocks; anddetermining the posture of the marker based on the determined locationof the sub-pattern.
 30. The method according to claim 26, wherein theone or more capturing units include two or more capturing units, or theone or more capturing elements include two or more capturing elements,and wherein the tracking the location and the posture of the markercomprises determining the location of the marker based on triangulationby using pattern images that are obtained by the two or more capturingunits or by the two or more capturing elements.
 31. The method accordingto claim 30, wherein the determining the location of the marker based onthe triangulation comprises determining the location of the marker basedon central coordinates of the pattern region on each of the patternimages and triangulation by using a geometric relationship betweendirections in which the two or more capturing units or the two or morecapturing elements view the marker.
 32. A computer-readable recordingmedium that stores a program that includes instructions for executingoperations of the optical tracking method according to claim 26.